1. Field of the Invention
The invention relates to an improved piezoelectric actuator useful, for example, for actuating a mechanical component such as a valve or the like.
It is generally known that the so-called piezoelectric effect can be used to produce a piezoelectric element partly comprised of ceramic material with a suitable crystalline structure. When an external electrical voltage is applied, a mechanical reaction of the piezoelectric element occurs, which produces a pressure or tension in a direction that can be predetermined as a function of the crystalline structure and the regions to which the electrical voltage is applied.
2. Description of the Prior Art
The structure of these piezoelectric actuators can be laid out in a number of layers, in the form of so-called multilayered piezoelectric actuators in which the layers are respectively interspersed with the inner electrodes used to apply the electrical voltage. To this end, piezoelectric sheets are produced and stacked in alternation with printed electrode surfaces that serve as inner electrodes. In this case, a sheet has its connection only on a connection side and on the opposite side, must have an edge without an electrode and this edge must be provided with an insulating space. Then the two sides are connected on the outside by means of outer electrodes. The piezoelectric actuator is thus produced in a known way with a number of plates, much like a capacitor.
Such multilayered piezoelectric actuators are operated with field intensities that require an insulation of the open leakage paths in the outer piezoelectric ceramic between the potentials of the outer electrodes. Suitable lacquers or insulating materials with favorable adhesion and favorable breakdown and insulation characteristics can, for example, be applied over a general area in an intrinsically known way, using proven methods that involve spraying or immersion.
Piezoelectric actuators of this kind are known, for example, from DE 199 28 190 A1, in which the outer electrodes are strengthened with reinforcing materials such as corrugated sheets or gratings and are provided for connecting inner electrodes to connections.
In order to assure a reliable manufacturing process in mass production, it is important to prevent contamination of the contact zones for the connection of outer electrodes, e.g. by means of welding or soldering. An above-described application of lacquer, however, may possibly lead to a contamination of the tools used in the connecting process. The required contaminant-free contact points, however, can only be achieved with difficulty, by removing lacquer and lacquer residues.
DE 199 28 180 A1 has also disclosed that in the region between the contacts of the outer electrodes, the piezoelectric layers are recessed toward the inside by a predetermined amount to form a groove. During machining of the piezoelectric actuator surface and during attachment of the outer electrodes, this groove prevents the electrode material between the outer electrodes from becoming smeared and therefore results in a significant improvement in the resistance of the piezoelectric actuator to insulation breakthroughs.